This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A057220 #13 Nov 25 2023 08:42:43
%S A057220 2,4,6,8,12,14,18,36,68,152,212,324,1434,1592,1668,3338,7908,9662,
%T A057220 27968,28116,33974,41774,66804,144518,162954,241032,366218,676592,
%U A057220 991968
%N A057220 Numbers k such that 2^k - 23 is prime.
%C A057220 Note that for the values 2 and 4 the primes are negative.
%C A057220 a(22) > 41358. - _Jinyuan Wang_, Jan 20 2020
%C A057220 All terms are even. - _Elmo R. Oliveira_, Nov 24 2023
%H A057220 Henri Lifchitz and Renaud Lifchitz, <a href="http://www.primenumbers.net/prptop/searchform.php?form=2%5En-23">Search for 2^n-23</a>, PRP Top Records.
%e A057220 k = 6: 2^6 - 23 = 41 is prime.
%e A057220 k = 8: 2^8 - 23 = 233 is prime.
%t A057220 Do[ If[ PrimeQ[ 2^n - 23 ], Print[ n ] ], { n, 1, 15000} ]
%o A057220 (PARI) is(n)=ispseudoprime(2^n-23) \\ _Charles R Greathouse IV_, Jun 13 2017
%Y A057220 Cf. A096502.
%Y A057220 Cf. Sequences of numbers k such that 2^k - d is prime: A000043 (d=1), A050414 (d=3), A059608 (d=5), A059609 (d=7), A059610 (d=9), A096817 (d=11), A096818 (d=13), A059612 (d=15), A059611 (d=17), A096819 (d=19), A096820 (d=21), this sequence (d=23), A356826 (d=29).
%K A057220 nonn,more
%O A057220 1,1
%A A057220 _Robert G. Wilson v_, Sep 16 2000
%E A057220 a(19)-a(21) from _Jinyuan Wang_, Jan 20 2020
%E A057220 a(22)-a(23) found by Henri Lifchitz, a(24)-a(27) found by Lelio R Paula, a(28)-a(29) found by Stefano Morozzi, added by _Elmo R. Oliveira_, Nov 24 2023